The propagation of Bleustein–Gulyaev waves in the presence of a dc electric field in the vacuum baked piezoelectric semiconducting crystals of class 6 has been studied theoretically. By solving the partial differential equations representing the electron–acoustic wave interaction in the piezoelectric semiconducting region, and the Laplace’s equation in the vacuum region separately and fulfilling the relevant boundary conditions, we obtain an expression for the amplification coefficient. The effects of carrier diffusion, resistivity, and carrier drift velocity on the amplification coefficient have been studied based on numerical calculations for the semiconducting CdS sample. It has been observed that, compared to Rayleigh waves, the Bleustein–Gulyaev waves give a much higher amplification.